The purpose of this procurement is to provide two contracts for rodent production centers to produce disease-free, genetically homogeneous and microbiologically defined rodents (F344 rats and B6C3F1 hybrid mice or other strains of rodents as required by the scientific decision of the Program) for the NTP toxicology research and testing program. Centralized colonies of disease-free, genetically homogeneous and microbiologically defined rodents will ensure an adequate and continuous supply of defined quality animals for the NTP toxicology research and testing program.